Method of and apparatus for measurement of blood flow using coherent light

An apparatus for measuring blood flow in a vascular bed, the apparatus comprising:

• means for illuminating a region of tissue having a vascular bed with coherent light;
• means responsive to light backscattered from the region of tissue for producing a broadened spectrum signal output;
• circuit means coupled to said means for producing a broadened spectrum signal output and responsive to its broadened spectrum signal output for producing a signal representative of the blood flow in the vascular bed;
• and
• means for collecting backscattered light from the region of tissue;
• wherein said means responsive to backscattered light comprise photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a mean current and having a substantially constant shot noise output S;
• wherein said circuit means comprise means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof, weighted detector means coupled to said photodetector and responsive to the broadened spectrum of low frequency signals for developing an output signal R;
• including calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the blood flow in the vascular bed, and
• a differentiator means and a low pass filter connected between said photo-detector means and said weighted detector means.

A method of measuring the blood flow in a vascular bed, the method comprising:

• illuminating a region of tissue having a vasuclar bed with coherent light;
• collecting at least some of the scattered light from the region;
• detecting the collected light to determine its broadened spectrum;
• and
• determining the blood flow in the vascular bed from said broadened spectrum;
• wherein said detecting step comprises non-linearly detecting the backscattered light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I;
• and wherein the determining step comprises producing a weighted output signal R from the broadened spectrum of low frequency signals, determining the shot noise constant S of the photo-detector, and producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I.

A method of measuring the blood flow in a vascular bed, the method comprising:

• illuminating a region of tissue having a vascular bed with coherent light;
• collecting at least some of the scattered light from the region;
• detecting the collected light to determine its broadened spectrum;
• determining the blood flow in the vascular bed from said broadened spectrum;
• wherein said detecting step comprises non-linearly detecting the backscattered light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I;
• and wherein the determining step comprises producing a weighted output signal R from the broadened spectrum of low frequency signals, determining the shot noise constant S of the photo-detector, and producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I;
• filtering the broadened spectrum of low frequency signals to pass only signals below a given frequency prior to detecting the broadened spectrum of low frequency signals;
• and
• differentiating the filtered low frequency signals with respect to time prior to detecting the broadened spectrum of low frequency signals.

An apparatus for measuring the flow of flowing material, the apparatus comprising:

• means for illuminating at least a portion of the flowing material with coherent light;
• means for collecting backscattered light from the material;
• photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a mean current and having a substantially constant shot noise output S;
• means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof;
• weighted detector means coupled to said photo-detector and responsive to the broadened spectrum of low frequency signals for developing an output signal R;
• and
• calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the flow.

An apparatus for measuring the flow of flowing material, the apparatus comprising:

• means for illuminating at least a portion of the flowing material with coherent light;
• means for collecting backscattered light from the material;
• photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a mean current and having a substantially constant shot noise output S;
• means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof;
• weighted detector means coupled to said photodetector and responsive to the broadened spectrum of low frequency signals for developing an output signal R;
• calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the flow;
• and
• a differentiator means and a low pass filter connected between said photo-detector means and said weighted detector means.

A method of measuring the flow parameter of flowing material, the method comprising:

• illuminating at least a portion of the flowing material with coherent light;
• collecting at least some of the light scattered from the material;
• non-linearly detecting the collected light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I;
• detecting the broadened spectrum of low frequency signals to produce a weighted output signal R;
• determining the shot noise constant S of the photodetector;
• and
• producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I.

A method of measuring the flow parameter of flowing material, the method comprising:

• illuminating at least a portion of the flowing material with coherent light;
• collecting at least some of the light scattered from the material;
• non-linearly detecting the collected light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I;
• detecting the broadened spectrum of low frequency signals to produce a weighted output signal R;
• determining the shot noise constant S of the photo-detector;
• producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I;
• wherein the step of detecting the broadened spectrum of low frequency signals comprises detecting the broadened spectrum of low frequency signals to produce a root-mean-square output signal R;
• filtering the broadened spectrum of low frequency signals to pass only signals below a given frequency prior to detecting the broadened spectrum of low frequency singals, and
• differentiating the filtered low frequency signals with respect to time prior to detecting the broadened spectrum of low frequency signals.